Toxic Metabolites and Inborn Errors of Amino Acid Metabolism: What One Informs about the Other

Abstract

In inborn errors of metabolism, such as amino acid breakdown disorders, loss of function mutations in metabolic enzymes within the catabolism pathway lead to an accumulation of the catabolic intermediate that is the substrate of the mutated enzyme. In patients of such disorders, dietarily restricting the amino acid(s) to prevent the formation of these catabolic intermediates has a therapeutic or even entirely preventative effect. This demonstrates that the pathology is due to a toxic accumulation of enzyme substrates rather than the loss of downstream products. Here, we provide an overview of amino acid metabolic disorders from the perspective of the ‘toxic metabolites’ themselves, including their mechanism of toxicity and whether they are involved in the pathology of other disease contexts as well. In the research literature, there is often evidence that such metabolites play a contributing role in multiple other nonhereditary (and more common) disease conditions, and these studies can provide important mechanistic insights into understanding the metabolite-induced pathology of the inborn disorder. Furthermore, therapeutic strategies developed for the inborn disorder may be applicable to these nonhereditary disease conditions, as they involve the same toxic metabolite. We provide an in-depth illustration of this cross-informing concept in two metabolic disorders, methylmalonic acidemia and hyperammonemia, where the pathological metabolites methylmalonic acid and ammonia are implicated in other disease contexts, such as aging, neurodegeneration, and cancer, and thus there are opportunities to apply mechanistic or therapeutic insights from one disease context towards the other. Additionally, we expand our scope to other metabolic disorders, such as homocystinuria and nonketotic hyperglycinemia, to propose how these concepts can be applied broadly across different inborn errors of metabolism and various nonhereditary disease conditions.

Non‐Hodgkin lymphoma in a kidney transplanted patient with methylmalonic acidemia: Metabolic susceptibility and the role of immunosuppression

“…MMA induces SOX4 by activating autocrine TGFß signaling, resulting in transcriptional reprogramming of cancer cells that endows them with malignant properties such as invasiveness and metastatic potential. For example, MMA can induce a pro‐metastatic epithelial‐to‐mesenchymal transition‐like phenotype, with a decline in E‐cadherin and a concurrent increase in fibronectin and vimentin 35,36 …”

“…For example, MMA can induce a pro-metastatic epithelial-to-mesenchymal transition-like phenotype, with a decline in E-cadherin and a concurrent increase in fibronectin and vimentin. 35,36 Several factors may increase the risk of PTLD. In early post-transplantation onset PTLD, the induction therapy and the EBV infection are the most important.…”

“…For example, MMA can induce a pro‐metastatic epithelial‐to‐mesenchymal transition‐like phenotype, with a decline in E‐cadherin and a concurrent increase in fibronectin and vimentin. 35 , 36 …”

Late-onset cobalamin C deficiency type in adult with cognitive and behavioral disturbances and significant cortical atrophy and cerebellar damage in the MRI: a case report

“…The diagnosis of late-onset cblC deficiency in adults was confirmed through genetic testing. MMA, also known as methylmalonic aciduria, is a congenital organic acid metabolic disease with multifactorial autosomal recessive inheritance (7). Various genetic defects in methylmalonic acidemia and homocysteinemia, involving cobalamin metabolism, have been identified, including cblC, cblD, cblF, cblJ, and cblX, with cblCdeficient disease being the most prevalent (8).…”

Methylmalonic acidemia: Neurodevelopment and neuroimaging

“…10.3389/fnins.2023.1110942 2. Etiology and pathogenesis of MMA Methylmalonic acidemia (MMA) is the most common type of congenital organic acidemia (Lee and Kim, 2022). It is mainly caused by the deficiency of methylmalonyl-coenzyme A mutase (MCM) or abnormal metabolism of adenosylcobalamin.…”